The present invention relates to an electrical capacitor of variable capacitance, and particularly to such a capacitor which uses liquid dielectrics to establish the varying capacitance. In particular, the invention relates to such a capacitor wherein the body of dielectric material of the capacitor is comprised of a densely sintered ceramic material.
One variable capacitance capacitor is known from German Provisional Patent De-AS No. 11 05 519. However, its two capacitor plates are self-supporting capacitor plates which are rigidly connected to each other. The space between the rigidly connected capacitor plates is filled up to a variable height by a first liquid dielectric of high dielectric constant. Above this first liquid dielectric there is a second liquid dielectric of lower density and lower dielectric constant. The capacitor plates can be provided with an insulating coating, for instance an insulating varnish, in order to increase the breakdown strength. To serve as the liquid dielectric of high dielectric constant, use is made, for instance, of oil, glycerine, distilled water or else a mixture of distilled water and glycerine or chlorine derivatives of benzene and diphenyl, for instance chlophene. To serve as the liquid dielectric of lower density and smaller dielectric constant, a light oil can be used. The capacitor plates are arranged in a container. No detailed information is given in this patent as to the construction of the arrangement.
Also known is a liquid-cooled, variable vacuum capacitor with stationary electrodes, which are movable at one end within a vacuum-tight housing with movable electrodes which are interleaved with the stationary electrodes and which electrodes are movable by mechanical means in the axial direction with respect to the stationary electrodes. This is known from German Application for Patent DE-OS No. 20 63 885. This variable vacuum capacitor and the capacitor known, for instance, from German Application DE-OS No. 22 59 351 are constructed in mechanically expensive fashion from a large number of parts, making these vacuum capacitors relatively expensive. Furthermore, their mechanical parts are subject to wear upon repeated adjustments of their capacitance. The period of use of vacuum capacitors in operation is also limited by the fact that the vacuum and thus the dielectric strength drops after a longer period of time, which can lead in the extreme case to the failure of the capacitor.
German Application DE-OS No. 22 39 220 discloses a variable capacitor consisting of a dielectric cylinder on which an electrically conductive layer is arranged on a part of its outer cylindrical surface. That layer forms a first capacitor plate. A ram which is arranged for axial movement within the dielectric cylinder forms the second capacitor plate. This known capacitor has chambers which are filled with a liquid dielectric.
German Utility Mode DE-GM No. 17 26 891 discloses a ceramic capacitor with liquid cooling, particularly for high-frequency industrial generators. At least the part of the ceramic dielectric is covered by the metal layers of the plates. The dielectric may also have a tubular development, and it forms or it has a hollow space to receive the cooling liquid. Cooling liquids suggested in general are water, oils, cooling brines or other non-conductive liquids. However, there is no indication of two different, non-intermixing dielectric liquids and thus no suggestion as to the development of a capacitor of variable capacitance.